Efficient electric boat

Discussion in 'Boat Design' started by Jeremy Harris, Jun 22, 2009.

  1. John in CR
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    John in CR Junior Member

    yellow cat,

    Compared to everything else marine related, the cost of batteries, motor, controller along with a solar charging rig can be relatively insignificant. Your mention of a live aboard craft sitting still the vast majority is a big part of keeping it inexpensive. Sure batteries will be expensive if you need big capacity for cruising continuously on electric power for long distances, but solar can assist in a big way in that regard given the low power requirements to push a sailing cat as long as you stay well below hull speed.

    Were you looking at marine electric propulsion units, or DIY with a few kw peak power in each hull and drive shafts already in place? From the sound of it, even just a pair of cheap trolling motors stowed away when under sail and smallish battery pack will meet your needs.
  2. yellow cat
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    yellow cat Junior Member

    Hi John
    thanks for the feedback. I called Torquedo to get a ball park figure for their new ocean outboards. and batteries. this is more than the cost of materials for the whole boat. (wood epoxy) and more. Prices will go down and new battery technology is setting roots.
    In the mean time i am trying to parallel the human factor for propulsion . It may sound ridiculous , it was at first, but pushing a 60 ft cat, (15 tons) + , with gas at 8 knots we can pay 10-15 Ca$ / h. . We pay more for our wakeboats but we intend to make waves for surfing at 11 knots ich.. Here we have to earn almost double the net cost of expenditures. Close to 90% taxes on gas cost. In Venezuela it is a different story ...
    If one can work it out for 4 hrs , that is a potential for 32 miles, a frequent day distance in the carribeans ... but they have those trade winds ...
    In fact, when we work to pay gas, we end up storing energy in the form of cash. We put that energy in a container for later use. My friend paid 1500 $ + in gas for an excursion from Montreal to québec city , about 150 miles. He was going 25 mph (he talks in MPH) pretty much the whole way with his 37 ft Fourwin cruiser .
    We dont see humans pushing boats because they can't ... i was not surprised to hear how powerfull a normal , in shape , man can produce with his total muscular capacity.
    We are of course limited by the hump speed. But could we be on top of that surfing speed compounded with gas or electric propulsion. I think windage will then be the ultimate barrier. We are not far from hovercrafting . The ultimate machine for many reasons.
    Back to work.
  3. John in CR
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    John in CR Junior Member

    Dismissing electric drive based on Torqueedo's high end marine type pricing is a mistake, but not as bad as your human powered 15 ton boat idea. If you want to push it past hull speed, then forget about electric because the power requirement will require a silly amount of battery.
  4. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    An average healthy man will have a power output somewhere between 100 and 150 W over a couple of hours period. So two men could produce 300 W.

    Considering a prop+gearing efficiency of 0.7 (if well-designed), two persons could push a 60 ft cat at a speed of 1.5-1.6 kts approximately.

  5. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    It's been done, here's an old post from the human powered boats forum (links no longer active):

    In the event you get around to thinking about propeller systems
    again. You may be interested in something I made for a large
    catamaran. There is a particular yacht race here where human power
    is permitted as it is a combination of sailing and athletics (running
    up mountains) - called the The Three Peaks Race.

    I mounted a gearbox with pedals over the stern of the catamaran using
    a curved shaft. Picture here:
    I initially tested it with an 800mm diameter large model plane prop
    and had buckling issues with the curved shaft due to the high thrust
    load and low rpm. I then reduced the flexible portion of the shaft
    to about 1500mm and mounted this off a 1200mm length of aluminium
    tube. For this shaft configuration I made a 4-bladed lightweight
    metal prop that was 600mm diameter.

    In testing with the latter set up I got the 8 tonne catamaran to
    2.7kts working within my aerobic limit. It was surprising how much
    difference having a dagger board partially lowered made to the drag
    due to the offline thrust. This was in line with my prediction and
    translates to 4kts with two drives.

    This year the pedal system was used in conjunction with oars. The
    pedal system was as effective as two rowers while adding the pedal
    power to the rowers increased speed by about 50%.

    The catamaran owner has since asked me to make a system using two
    gearboxes similar to this one:
    This unit was made for a 400kg boat and has got that to 6kts - all
    day speed is around 4kts. The unit for the catamaran will have a
    bigger prop and deeper leg. It will be more compact for storage
    purposes than the long curved shaft. If it tests out well then there
    will be one made for each hull.

    I am able to do quite accurate performance predictions for these
    systems based on the hull shape, displacement and the drive system
    design. For a small yacht you could get quite good results sitting
    across the cockpit with a drive leg below the hull and prop driven
    directly by a chain. There are some very economical model plane
    props. This one is similar to the big one I used initially:

    Rick Willoughby

    This message comes to you via the hpv-boats@bikelist.org mailing list, sponsored by http://www,HuPI.org/
    Visit http://bikelist.org/mailman/listinfo/hpv-boats to manage your subscription.

    Scroll down on this link for a long distance picture of the setup:


  6. yellow cat
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    yellow cat Junior Member

    Thanks for the info. The idea is to get mechanical power stored. There are few ways to do it. Either lift loads up a mast , stretch bungies . All of this would be done when the cat is at rest. Using human strength, tidal force, wind force (pulling on the anchor/mooring chain) . The idea to use only a man rowing or padling is not enough for interesting performances. There is the slip at the prop pitch, and the loss of energy due to energy transfer to the substrate , if we can call it that. But those lost can be minimised with a ring around the props with a foil shape, that should be good for up to 6 - 8 knots . The good old wheel or blade fins used by Hobie Cat on kayaks. We use a twin seater trimaran kayak, i don't know if it is more efficient than a ring prop, but we like to push it to the limit. We combined our arms to our legs, but we would need bigger fins .
    Again, this is for few hours or even minutes source of energy. Nothing seems to beat a combustion engine at the right rpm, for moving and heating water.
    Time to have breakfast.
  7. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I'm not sure what you mean by this.
    Are you going to turn into a newt?
  8. yellow cat
    Joined: Mar 2009
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    yellow cat Junior Member

    when you push and pull the fin gizmo, it is possible to "help" your legs by adding tension bars at the end of the foot bars. We would add some length perhaps in order to multiply the arms force. Like at the gym, it exercises arms and legs, i forget the name.
    This can perhaps increase power significantly, obviously only one of the two paddlers can do it, the other needs his arms to steer. We think we could increase the fin areas by 50%.
    It will give more tork so top speed would not be increased by more than a couple knots , if that. The problem we find is in shallow waters, on top of which we keep braking the plastic "sacrificial " pin at the rudder. But it is a lovely toy from which i think i can develop. Check it out on Hobie's web site.
  9. kerosene
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    Location: finland

    kerosene Senior Member

    Hobie flippers as well as a wheel will have worse efficiency than a well designed prop. Watt is a watt no matter if its a man, electric motor or gasoline motor.

    Few hundred watts will not do miracles on a big boat. There is no magical leaps to be made in a big boat.
  10. kerosene
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    kerosene Senior Member

    Also, using both arms and legs / whole body can give higher peak power for short bursts but long term lungs and body's energy system are limiting factor. Legs are enough to exhaust the body's energy peoducing capacity. Fir trips over a few minutes using whole body will not make a difference in total output.
  11. yellow cat
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    yellow cat Junior Member

    And a well hydrodynamicly designed hull will be easy to move. I met an owner of a large trimaran in Florida who got towed and the towing boater could not beleive how little it affected his engine at low speed (5-6knots) . I found those fins to be quiet in water. Shear is limited to a minimum. I forget how fast we went last time we had the gps , paddling with no wind. 17 km/h is pretty much the comfortable speed at sail, faster means alot of splash and work for a few knots. On the Nacra, 33-34 km/h are common, when we get to 38 + km/h, we notice alot more power is needed to gain 1 km/h, stronger winds and hence bigger waves ... I could not try to pull it yet, i'll have to get a 300 ft rope and try to run with it, pulling it in ... when we were young and restless, we ran pushing our fishing wooden boats, we were limited by our capacity to run faster in this shallow 1 ft deep low tide water, and slipery bottom. We did not have computers and smart phones then, we were more in shape i guess.
  12. Boucaneer
    Joined: Sep 2014
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    Boucaneer Junior Member

    I'm very interested in the these longtail cordless drill trolling motors.
    I'm planning to use a Dwalt 995 brushless cordless drill used at middle speed setting at 1,300 rpm with lithium batteries 18 v, 5 amp hour x 4 for the power source.

    I'm just trying to remember what size remote control prop to use or what size trolling prop to purchase.

    Does anyone have any researched suggestions?

    It would be great to solar charge the spare lithium battery whilst under way in the boat with a sun shade solar panel, my canoes are open canoes at 15' LOA with 4' beam with a comfy sitting/sleeping area.

    It's a great idea I would like to accomplish, just researching what size prop to use, so any suggestions would be welcomly appreciated.
  13. Pericles
    Joined: Sep 2006
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    Pericles Senior Member

    Are we getting close to a decent battery pack?


    Boats, houses; stored electricity will be a game changer.


    Assuming the battery has around 1000 charge / discharge cycles, paying $3500 every 3 years is approaching price parity with some of the more ridiculous electricity utility charges. When you factor in the satisfaction of tearing up your last electricity bill, there is a real chance a significant number of people will be tempted to make the leap.

    How will utility companies respond? I suspect they will be forced to cap household bills, to put as much price distance as possible, between the Tesla option, and staying connected to their grid. It will no longer be possible to make electricity rates skyrocket, to treat household electricity consumers as an inelastic revenue source – because now householders have an alternative, to putting up with endless price rises.

    The biggest losers from this potential game changer, in my opinion, might be large scale renewable energy providers. Since households now have an alternative to paying ever larger electricity bills, electricity utilities will be forced to keep costs down – they will no longer be able to ignore costs imposed by government mandated renewable schemes. Either the government will be forced to provide higher subsidies, or large scale renewable schemes will have to be scaled back, to keep grid electricity price competitive.

  14. Dennis A
    Joined: Aug 2009
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    Location: Amersham bucks uk

    Dennis A Junior Member

    Prop for longtail

    Hi Boucaneer
    Sounds interesting, I assume that you are looking for lowish speeds. I would start with a 12" x 12" prop to see if this matches you boat,
    I know nothing about the Dewalt drill but you should check to see if it is suitable for continues duty. I am at present using a Makita 480 drill and it is fitted with a timer cutout that is set for 3 mins. This can be reset by switching off by it shows that the manufactures are not fitting continues rated parts.


  15. Boucaneer
    Joined: Sep 2014
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    Boucaneer Junior Member

    Thank you Dennis,

    I will certainly try the 12" x 12" prop, A good place to start, thank you.

    Well from my l
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